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AD9850 DAC output current boost


K5ESS
 

Thanks Jim,

Yes I have the APP Note on using the FET to modulate the DDC output.

 

Mike K5ESS

 

From: PHSNA@... [mailto:PHSNA@...]
Sent: Tuesday, December 08, 2015 2:52 PM
To: PHSNA@...
Subject: [PHSNA] Re: AD9850 DAC output current boost

 

 

I haven't played with R-set. There is a graph in the data sheet showing that the best spurious free dynamic range is at an I-out of 10 mA. Going to 20 mA degrades SFDR by a couple of dB or so. Would only add 5 mA to the average current, so I doubt heating would be an issue. Given the I-supply is around 80 mA, it would be about a 10% increase in dissipation.

Look in the Links area here on the group for an app note about replacing R-set with an FET to amplitude modulate the output (could be the basis of AGC)

Jim, N5IB



---In PHSNA@..., <k5ess.nothdurft@...> wrote :
The AD9850 datasheet says that the max DAC output current is 20mA which can be achieved by reducing the value of the R-SET resistor from 3.9k to 1.95k ohms.  Has anyone tried this and if so were there any deleterious effects? 


N5IB
 

I haven't played with R-set. There is a graph in the data sheet showing that the best spurious free dynamic range is at an I-out of 10 mA. Going to 20 mA degrades SFDR by a couple of dB or so. Would only add 5 mA to the average current, so I doubt heating would be an issue. Given the I-supply is around 80 mA, it would be about a 10% increase in dissipation.

Look in the Links area here on the group for an app note about replacing R-set with an FET to amplitude modulate the output (could be the basis of AGC)

Jim, N5IB




---In PHSNA@..., <k5ess.nothdurft@...> wrote :
The AD9850 datasheet says that the max DAC output current is 20mA which can be achieved by reducing the value of the R-SET resistor from 3.9k to 1.95k ohms.  Has anyone tried this and if so were there any deleterious effects? 


K5ESS
 

The AD9850 datasheet says that the max DAC output current is 20mA which can be achieved by reducing the value of the R-SET resistor from 3.9k to 1.95k ohms.  Has anyone tried this and if so were there any deleterious effects?  I assume it would run hotter.
Mike K5ESS